What is an MSF file?
An .MSF file is primarily a Mail Summary File used by Mozilla Thunderbird. It acts as an index that stores the headers and summaries of your email messages. It does not contain the actual email text. The emails are usually kept in a matching file without an extension. An .MSF file can also be an audio file from an Olympus or Sony voice recorder, a Zubersoft MobileSheets setlist file, or a Miranda IM skin file.
How to open MSF files?
You can use Mozilla Thunderbird to rebuild or read the email index. Because the index is stored as plain text, you can inspect it with Notepad++ or Visual Studio Code. Voice recordings must be opened with the manufacturer software.
Best practices and troubleshooting
If your inbox shows incorrect emails, deleting the .MSF file forces the software to rebuild the index. Do not delete the accompanying mail file. If your .MSF file is a voice recording, try converting it to a standard audio format.
Summary
Because .MSF has multiple possible meanings, we recommend using viewer.online/msf to identify the actual format of your file. viewer.online/msf analyzes .MSF files to identify their exact format and creator software, shows which programs can open the file, and usually previews it directly in the browser, eliminating the need to install software or troubleshoot compatibility issues. If you need to convert your file to another format, such as changing an audio recording to MP3, use convert.guru.